In This Issue developed differently and far less Shaken Structures effectively." He has aJso served Jim Beck and John Hall, both as division chairman (1963- 68) assistant professors of civil and provost and vice president engineering, visited Mexico City (1980-83). 12 days after the September 19 earthquake. Although they couldn't get into all the struc­ tures simply by donning hard Spaceman Wang hats and trying to appear official, As the first (and only) scientist­ their four days of observations astronaut from Caltech's Jet Pro­ provide some interesting insights pulsion Laboratory to fly on the into why buildings failed. These space shuttle, Taylor Wang has are described in «Engineering been in great demand to recount Features of the Recent Mexican his experiences - including a Earthquake," which starts on warm welcome in his native page 2. Unofficial though their China. His good-natured wit in investigations were, they may be describing his life as an astronaut of particular importance since delighted his Watson Lecture few official engineering studies audience at Cal tech last October; were done in the rush to clear Magnetic Magic that talk, "A Scientist in Space," away the ruins. And the struc­ On the cover - an NMR image is adapted here beginning on tural failures in Mexico City will of the brain in transaxial section page 17. force a closer look at other areas taken through the middle of the Born in Shanghai, Wang that may have similar soil eyeballs and ears. The colors are came to the United States via characteristics. false, and their gradations from Taiwan and earned his BS, MS, Hall received his BS from white through magenta to red to and PhD degrees in physics at West Virginia University (1972), black represent combinations of UCLA. He's MS from the proton density and rates of worked at JPL University of relaxation by which NMR since 1972 Illinois (1973) differentiates among various where early on and PhD from kinds of tissue. NMR stands for he recognized UC Berkeley nuclear magnetic resonance, a the potential (1980). He's laboratory technique used for 40 of zero gravity been at Cal­ years to study a wide variety of in doing con- tech since molecular properties. In Lk I tainerless 1980. "Biomedical Applications of experiments. He invented the NMR," beginning on page 10, acoustic levitation and manipu­ Institute Professor of Chemistry lation chamber in the drop John D. Roberts explains how dynamics module for investigat­ NMR works and how the tech­ ing fluid behavior in space. nique has been applied in recent When this experiment balked on years to the imaging of biochem­ Spacelab 3, Wang spent 2 ,(, ical processes in human beings. days inside the apparatus in a The article was adapted from his heroic rescue - justifying Seminar Day talk last May. ~ASA's decision to put scientists Roberts is one of the pio­ In space. neers of NMR applications to chemistry and biochemistry. STAFF: Editor - Jane Dietrich After earning Writer - Robert Finn his BA (1941) Production Artist - Barbara Wirick and PhD Photographer - Robert Paz (1944) from UCLA, PICTURE CREDITS: Cover, 12, 14, 16 - HMRI; 10, 14, 15 - General Roberts came Electric Company; 11-14, 16 - Rose Meldrum; 2, 6-9 - John Hall, Jim to Caltech in Beck; 17-23 - NASA; 31 - Eleanor Helin; 32 - JPL 1952 and has been professor since 1953. His work demon­ Engineering & Science (ISSN 0013-7812) is published five times a year, September, strated with extraordinary clarity November, January, March, and May, at the California Institute of Technology, 1201 the power of NMR as a tool for East California Boulevard, Pasadena, California 91125. Annual Subscription $7.50 domestic, $20.00 foreign air mail, single copies, $1.50. Third class postage paid at studying molecular structure and Pasadena, California. All rights reserved. Reproduction of material contained herein dynamics. Said a colleague, "If forbidden without authorization. Cl 1986 Alumni Association California Institute of Roberts had not entered the field Technology. Published by the California Institute of Technology and the Alumni of NMR at an early stage, I Association. Telephone: 818-356-4686. believe that the field would have Postmaster: Send change of address to Caltech, 1-71, Pasadena, CA 91125. ENGNE~~~~ CALIFORNIA INSTITUTE OF TECHNOLOGY JANUARY 1986 VOLUME XLIX, NUMBER 3 Engineering Features of the Recent Mexican Earthquake - by James L. Beck and John F. Hall Page 2 Caltech civil engineers document the extensive damage to modern multi-story buildings located on Mexico City's dry lake bed. Biomedical Applications of NMR - by John D. Roberts Page 10 A laboratory technique for studying molecular properties now offers great potential in medical imaging. A Scientist in Space - by Taylor Wang Page 17 A JPL physicist travels out of this world to do his experiments in zero gravity. Tiny Tale Gets Grand Page 24 Electron beam lithography reduces a page of Dickens to micrometer size to meet a long- standing challenge. Departments Research in Progress Page 27 Comet Composition To Shop or Not to Shop Random Walk Page 31 terns, on the other hand, fared well. The sub­ way and the international airport were func­ tioning again soon after the earthquake. Long-distance telephone transmissions were interrupted because of the collapse of the office building housing the equipment, but the local telephone system still worked. Utili­ ties also suffered only minimal damage. Water supplies eventually ran short because of damage to the distribution pipelines in the eastern and southeastern regions, but electri­ cal power continued to flow to most of the city. The collapsed Regis Hotel was the source of the only major tire from gas leak­ age, although a number of smaller tires broke out elsewhere. The earthquake occurred at 7: 18 a.m. on Thursday and had a Richter surface wave magnitude of Ms-8.1. A large aftershock of magnitude Ms=7.5 followed on Friday eve­ ning. The main shock was centered 250 miles from Mexico City on the Pacitic coast, near the town of Lazaro Cardenas on the Engineering Features border between the states of Michoacan and Guerrero (tigure I). The rupture zone extended for about 125 miles parallel to the coast along a tectonic feature called the Cocos of the Recent subduction zone, which stretches for more than 1,000 miles along the Pacific coast of Central America. This feature is the source of many large earthquakes that have shaken the Mexican Earthquake central and southern parts of Mexico in this century, including the 1957 Acapulco quake (Ms=7.5) and the 1979 Petatlan event (Ms-7.6), both of which produced serious damage in Mexico City. In this subduction zone, part of the floor of the Pacific Ocean, called the Cocos plate, is being forced under the landmass of Mexico, which lies on the North American plate. This is happening at a rate of about three inches by James L. Beck and John F. Hall per year. This relative motion builds up large strains at the interface of the two plates where they are locked, and the earthquakes result The unique mid-level col/apse HEEARTHQUAKEOFSEPTEMBER 19, 1985 pro­ from episodic release of the strain energy by of the hotel shown above may T duced the worst earthquake disaster in localized rupturing of the interface. Primarily have resulted from a discon­ Mexican history. Mexico City, although not on the basis of this simple physical model, tinuity in the slruclllral sys­ tem. This case presented devastated, sustained a huge blow in which as some seismologists had anticipated that a quite a dilemma for the many as 10,000 lives may have been lost. major earthquake would eventually occur in demolition crew, because the About 250,000 people, of a population of 18 the area of the recent event. They had horel is leaning over a row of million, lost their dwellings, and more than labeled this area the Michoacan seismic gap, undamaged apartment build­ 300 multi-story buildings either collapsed or because it had not ruptured completely for ings in the rear. The leaning portion a/the structure was were seriously damaged. Public buildings, more than 70 years, while neighboring regions finally removed piece by piece. such as schools, hospitals, and some govern­ had produced earthquakes several times dur­ ment housing projects, were particularly hard ing this period. For the same reason, a major hit, resulting in a large loss of life. earthquake is expected to occur eventually in Transportation and communication sys- the Guerrero gap, which lies between the rup- 2 ENGIN EERI N G &SCIENCE I JANUARY 1986 ture zones of the 1979 Petatlanand 1957 COLIMA )) Acapulco' earthciuakes. In such an event, .r__ r-_ J structural damage is likely to occur once + MICHOACAN + again in Mexico City. We visited Mexico City 12 days after the September earthquake and spent four days walking around the city observing the damage to buildings. Although we found it informa­ tive, there are limits to what we could learn in this way. The collapsed buildings, for example, left little visual evidence of the weaknesses that had precipitated their col­ lapse, and it was difficult to gain entry to seri­ o 50 ously damaged buildings to inspect their inte­ I, !!! km riors. But what really stood out was the o Acc<:)13fograph 3ite extent of the damage to modern multi-story * Epicenter buildings, which is perhaps unprecedented. A I03"W 102" 100'" survey by engineers from the National Auton­ omous University in Mexico City (UNAM) Figure 1 (above): Map show­ revealed that buildings of 6 to 15 stories sus­ ing the preliminary epicenters tained most of the damage. Distribution of of the main shock and largest aftershock relative to Mexico severe structural damage throughout Mexico City.